There are no "correct" designs for Leonardo da Vinci's machines. There are only solutions based on different interpretations of his drawings. Il Cigno -- "The Swan" -- was designed to show what Leonardo could have done if he focused on the problem of manned flight rather than moving on to other challenges. He had the necessary knowledge of structures and aerodynamics to make a machine like this one.
The pilot pulls the wings down by pushing with his arms and legs, air pressure pushes the wings back up. The moveable tail, actuated by the pilot's body movements, controls pitch and yaw during gliding flight.
Il Cigno is not a slavish reproduction of one of Leonardo's sketches. The builders of this aircraft replica concluded that Leonardo's sketches were simply a thinking process, never intended to be made into working machines. Leonardo knew that he had not solved the problem. The wide variety of designs and unfinished drawings tend to support this conclusion. His sparing collection of manned flight studies contributed little to advance the dream of flight except to announce that the most celebrated thinker of the age did not find the idea of flight ridiculous.
No modern materials or manufacturing techniques were used to build Il Cigno. Wood dowels and rawhide fasten the members together. The structure is white oak, a wood common to the Mediterranean.
An ornithopter is a machine shaped like an aircraft that is held aloft and propelled by wing movements. No successful man-powered ornithopter has ever been built and likely never will be. This is because man's musculature and metabolism are woefully inadequate for the job. A bird has some 60 percent of his weight devoted to the muscles which operate his wings, a huge lung capacity to sustain prolonged flight, and hollow, lightweight bones. Il Cigno could make a respectable glider and with a brave, strong, and very light pilot, it might achieve a couple of wing flaps during a flight.